Table of Contents
Journal of Amino Acids
Volume 2016 (2016), Article ID 8952520, 13 pages
http://dx.doi.org/10.1155/2016/8952520
Review Article

Tryptophan Biochemistry: Structural, Nutritional, Metabolic, and Medical Aspects in Humans

1Department of Clinical and Experimental Medicine, University of Pisa, 56126 Pisa, Italy
2Department of Pharmacy, University of Pisa, 56126 Pisa, Italy
3Interdepartmental Center of “Nutraceutical Research and Food for Health”, University of Pisa, 56124 Pisa, Italy

Received 7 September 2015; Accepted 6 December 2015

Academic Editor: Arthur Conigrave

Copyright © 2016 Lionella Palego et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

L-Tryptophan is the unique protein amino acid (AA) bearing an indole ring: its biotransformation in living organisms contributes either to keeping this chemical group in cells and tissues or to breaking it, by generating in both cases a variety of bioactive molecules. Investigations on the biology of Trp highlight the pleiotropic effects of its small derivatives on homeostasis processes. In addition to protein turn-over, in humans the pathways of Trp indole derivatives cover the synthesis of the neurotransmitter/hormone serotonin (5-HT), the pineal gland melatonin (MLT), and the trace amine tryptamine. The breakdown of the Trp indole ring defines instead the “kynurenine shunt” which produces cell-response adapters as L-kynurenine, kynurenic and quinolinic acids, or the coenzyme nicotinamide adenine dinucleotide (NAD+). This review aims therefore at tracing a “map” of the main molecular effectors in human tryptophan (Trp) research, starting from the chemistry of this AA, dealing then with its biosphere distribution and nutritional value for humans, also focusing on some proteins responsible for its tissue-dependent uptake and biotransformation. We will thus underscore the role of Trp biochemistry in the pathogenesis of human complex diseases/syndromes primarily involving the gut, neuroimmunoendocrine/stress responses, and the CNS, supporting the use of -Omics approaches in this field.